Yellow flag iris is native to Europe, Asia and north Africa. Introduced to New Zealand as an ornamental garden plant, it was first recorded growing wild in the Hutt Valley in 1938. It is present at isolated sites throughout New Zealand, but is currently banned from sale, propagation and distribution.
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Yellow flag iris forms dense stands that can displace native species and restrict access for recreational activities. Some infestations are the result of deliberate plantings, but most spread is by prolifi c seeding or by fragmentation of root rhizomes (horizontal stems that send out roots and shoots). It can also invade and displace low-lying pasture, and is toxic to livestock. The largest established stands grow on both sides of the Waikato River, particularly downstream of Ngaruawahia, but the species is also establishing elsewhere. It typically inhabits the margins of lakes, rivers or drains.
Yellow flag iris is a leafy wetland-terrestrial iris that grows up to 2 m. Forms dense floating mats in shallow water. It has thick creeping rhizomes with many rootlets. Plants die back in winter.
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Large yellow flowers from September to December. Flowers are up to 120 mm in diameter and are typically iris-like in form.
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Can be found on margins of still, fresh or slightly salty water such as rivers, swamps, salt marshes, pond edges. Tolerates frost, flooding, drought, high or low water fertility and many soil types.
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Seed capsules contain many smooth, flattened seeds which float on water.
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Broad flat sword shaped leaves, in fans from reddish base. Leaves are 20–30 mm wide, with a distinct mid-rib.
In all parts of the Waikato region, land occupiers are responsible for the total control of yellow flag iris on their property. If the land is less than 20 m from a waterway, control may be undertaken subject to an approved Environment Waikato programme. Yellow flag iris is banned from sale, propagation, distribution and commercial display.
Herbicide control
'Weed wipe’ or spray with glyphosate (such as roundup) or metsulfuron (such as escort) plus a penetrant (such as Pulse). Smaller infestations may be controlled by ‘injecting’ herbicide into the rhizome.
Follow-up control work is likely to be required.
When using herbicides:
• read the instructions on the manufacturer’s label closely
• always wear protective clothing
• always minimise the risk to desirable plants
• contact the supplier for further advice.
Note: If applying herbicide over water, a resource consent may be required. Please check with Environment Waikato before proceeding.
Useful contacts
For further information and advice contact your local Biosecurity Plant Pest Contractor.
For enquired on policy and procedural matters call Environment Waikato's Freephone 0800 800 401
For more information on plant pests, please visit the Weedbusters website.
Visit our Waikato Regional Pest Management Strategy.
'What makes a pest a pest? - A guide to Waikato's pest management future' download (730 kb, 104 seconds to download, 56k modem), order or pick up for free from our offices.
Pick up or order 'Plant me instead - Plants to use in place of common pest plants' for free from our offices.
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Pick up or order 'Poisonous plants and fungi in New Zealand - A guide for parents, schools and child minders' for $15 from our offices.
Disclaimer
Although this content has been prepared in good faith from a number of sources believed to be reliable, Environment Waikato does not give any warranty that all information contained is accurate or complete, or that advice given will be appropriate in all circumstances. Mention of product trade names implies neither endorsement of those products nor criticisms of similar products not mentioned.